Severe acute asthma is a medical emergency that must be quickly diagnosed and treated. Initial treatment includes a bronchodilator agent and systemic corticosteroids. In severe cases with poor response to the standard treatment, intravenous magnesium sulfate is a therapeutic option. This article aimed a literature review on the use of intravenous magnesium sulfate in the emergency room treatment of children with acute asthma. The treatment parameters of effectiveness, indication, dosage, adverse effects and contraindications were assessed. A narrative review of the literature based on a search of the Medline and Lilacs databases and the Cochrane Database of Systematic Reviews for articles published between 2000 and 2010 was conducted. The keywords used included the following: asthma, children, emergency and magnesium sulfate. Eight controlled clinical trials, three meta-analyses, one retrospective study, eight review articles and one cross-sectional study were included. A total of 21 articles were analyzed. Several authors reported that intravenous magnesium was effective in the treatment of acute asthma in children. Adverse effects were rare. The use of intravenous magnesium sulfate was indicated for patients with moderate to severe acute asthma not responding to initial treatment with a bronchodilator agent and systemic corticosteroids. Few contraindications were reported but included kidney failure and atrioventricular block. Reports of adverse drug interactions with magnesium were rare. Although reported as safe, intravenous magnesium is infrequently used in children with acute asthma. Most often it is used in severe, progressed cases to prevent respiratory failure and/or admission to the intensive care unit. Intravenous magnesium was concluded to be effective and safe in children with severe acute asthma, although its use in the emergency room is still limited.